Ethereal Investigator definitely allows you to do that, and if you can manage to blink it does it super well
He'd been trying to take advantage of Master of Cruelties, a card that had captured the imaginations of more than a few readers, and realized that Master of Cruelties doesn't actually need power to reduce an opponent to 1 life (although it's certainly worse against creatures if it doesn't have any), so he could use Heartless Summoning to play Master of Cruelties, since he was planning to make it unblockable with Rogue's Passage anyway
There's no other card that gives you two mana for one with no downside, and this ultra-consistent ramp card can go in any EDH deck, making it an auto-include for most people who aren't making a conscious effort to be hipster
The Ancient One doesn't even need to attack to put pressure on the opponents, since its deck will cheaply discard and mill huge creatures, then bring them back for combat
Ob Nixilis, the Adversary only lets you draw cards with its final ability, which can take a while to get to
ProxyKing cards are not official Magic: The Gathering cards and are not legal for Wizards-sanctioned tournaments